This would be very much a moving target. A significant amount of Meta's valuation is in "intangibles" which is an accounting category that is always subject to radically different valuations depending on whether you're inside or outside the company. 

It is too simple to look at FB's capitalization and divide by the FB user base population. There are some additional complexities in a case like this. 

At some point if enough liability cases resulted in rulings with significant cash payouts, lenders and investors will start demanding a much more detailed accounting of what assets there are as collateral for lending to Meta. At the point this would happen, a significant amount of intellectual property and proprietary information would have to come into discovery, else they would effectively be downgraded. Some of this disclosure could result in additional liabilities, especially if there are aspects of their algorithms in their software that increase the propensity for "screen addiction" by users. If such algorithms were found, the floodgates of litigation could open, and there would likely be a very large class action suit, much like there was against the tobacco companies. The tobacco companies never went bankrupt, they just had to raise prices significantly to cover the awards. 

It is worth noting that Meta lost a tax case vs. the IRS last year about valuation of assets they transferred into an Irish subsidiary.